Certain electronic components, such as field effect transistors, include a semi-conductive substrate having two distinct diffusion regions. The diffusion regions are generally referred to as a source and a drain. A gate is positioned adjacent the substrate between the source and the drain. Imparting a voltage to the gate sets up an electric field that enables current flow between the source and the drain through a channel in the portion of the substrate adjacent the gate. The substrate typically comprises a bulk monocrystalline silicon substrate having a relatively light concentration of a conductivity enhancing dopant impurity. In other configurations, the substrate comprises a thin layer of lightly doped semi-conductive material disposed over an underlying insulating layer. Such structures are commonly referred to as semiconductor-on-insulator (“SOI”) constructions.
As integrated circuit (“IC”) designs become more dense, the length and size of the channel becomes smaller. In addition, the junction depth, which is the thickness of the source or drain, also becomes smaller. As IC features such as channel length, channel size and junction depth become smaller, certain unwanted side effects can occur. For example, a small channel will increase the lateral electric field within the substrate, which can lead to performance degradation. Additionally, small junction depths can prevent adequate silicon consumption during a self aligned silicide (“SALICIDE”) process.
To address these problems, an elevated source/drain (“ESD”) structure has been developed. In an ESD structure, a portion of the source and drain regions are elevated above the substrate. For example, a thin epitaxial layer of monocrystalline silicon can be selectively grown from exposed monocrystalline silicon source and drain substrate areas. As used herein, “selective” growth includes, but is not limited to, growth only in particular regions of an underlying structure. For example, in certain applications, selective growth may occur only over non-oxide regions of a substrate, while non-selective growth would occur over an entire substrate, including oxide regions.
Epitaxial deposition of silicon is well known in the semiconductor device processing art, and involves the precipitation of silicon from a source gas onto a crystal lattice. The deposited silicon forms a structure that replicates and extends the underlying crystal lattice. Conventionally used silicon source gases include silane (SiH4), silicon tetrachloride (SiCl4), trichlorosilane (SiHCl3) and dichlorosilane (SiH2Cl2).
Additional background information on selective epitaxial deposition of silicon can be found in U.S. Pat. No. 4,578,142 to Corboy, Jr. et al., entitled “METHOD FOR GROWING MONOCRYSTALLINE SILICON THROUGH MASK LAYER” and filed on May 10, 1984. The entire disclosure of this patent is hereby incorporated herein by reference.
An ESD structure provides sufficient channel length to avoid unwanted side effects, despite the presence of a smaller (narrower) gate. Additionally, sufficient silicon consumption can be provided during the SALICIDE process.